The present invention relates to a phased array antenna used for transmitting/receiving an RF signal such as a microwave or milliwave to electrically adjust a beam radiation direction by controlling a phase supplied to each radiating element, and a method of manufacturing the antenna.
As a satellite tracking on-vehicle antenna or satellite borne antenna, a phased array antenna having many radiating elements arranged in an array has conventionally been proposed (see Technical Report AP90-75 of the Institute of Electronics, Information and Communication Engineers, and Japanese Patent Laid-Open No. 1-290301).
A phased array antenna of this type has a function of arbitrarily changing the beam direction by electronically changing the phase of a signal supplied to each radiating element.
As a means for changing the feed phase of each radiating element, a phase shifter is generally used.
As the phase shifter, a digital phase shifter (to be simply referred to as a phase shifter hereinafter) made up of a plurality of phase shift circuits having different fixed phase shift amounts is used.
The phase shift circuits are respectively ON/OFF-controlled by 1-bit digital control signals to combine the phase shift amounts of the phase shift circuits, thereby obtaining a feed phase of 0xc2x0 to 360xc2x0 by the whole phase shifter.
A conventional phased array antenna uses many components including semiconductor elements such as PIN diodes and GaAs FETs serving as switching elements in phase shift circuits, and driver circuit components for driving the semiconductor elements.
The phase shifter applies a DC current or DC voltage to these switching elements to turn them on/off, and changes the transmission path length, susceptance, and reflection coefficient to generate a predetermined phase shift amount.
Recently in the field of low earth orbit satellite communications, communications at high data rates are required along with the wide use of the Internet and the spread of multimedia communications, and the gain of the antenna must be increased.
To implement communications at high data rates, the transmission bandwidth must be increased. Because of a shortage of the frequency resource in a low-frequency band, an antenna applicable to an RF band equal to or higher than the Ka band (about 20 GHz or higher) must be implemented.
More specifically, an antenna for a low earth orbit satellite tracking terminal (terrestrial station) must satisfy technical performance:
Frequency: 30 GHz
Antenna gain: 36 dBi
Beam scanning range: beam tilt angle of 50xc2x0 from front direction
To realize this by a phased array antenna, first,
the aperture area: about 0.13 m2 (360 mmxc3x97360 mm) is needed.
In addition, to suppress the side lobe, radiating elements must be arranged at an interval of about xc2xd wavelength (around 5 mm for 30 GHz) to avoid generation of the grating lobe.
To set a small beam scanning step and minimize the side lobe degradation caused by the quantization error of the digital phase shifter, the phase shift circuit used for the phase shifter is desirably made up of at least 4 bits (22.5xc2x0 for the minimum-bit phase shifter).
The total number of radiating elements and the number of phase shift circuit bits used for a phased array antenna which satisfies the above conditions are given by
Number of elements for the phase shift circuit: 72xc3x9772=about 5,000
Number of phase shift circuit bits: 72xc3x9772xc3x974=about 20,000 bits
When a high-gain phased array antenna applicable to an RF band is to be implemented by, e.g., a phased array antenna disclosed in Japanese Patent Laid-Open No. 1-290301 shown in FIG. 19, the following problems occur.
More specifically, a conventional phased array antenna controls phase shift circuits in each phase shifter by one driver circuit formed on a driver circuit substrate, as shown in FIG. 19. For this purpose, the driver circuit must be connected to all the phase shift circuits.
This requires connection wiring lines equal in number to the number of radiating elementsxc3x97the number of phase shift circuit bits. If the above numerical values are applied, the number of wiring lines to phase shift circuits (4 bits) for one line (72 radiating elements) is 72xc3x974=288 in an array of 72xc3x9772 radiating elements.
If these wiring lines are formed on a single plane, the width of a wiring line bundle for one line (72 radiating elements) is 0.1 mmxc3x97288=28.8 mm for the wiring line width/wiring line interval (L/S)=50/50 xcexcm.
To the contrary, in a phased array antenna applicable to a frequency of 30 GHz, radiating elements must be arranged at an interval of around 5 mm, as described above. In the prior art, however, the wiring line bundle is as thick as 28.8 mm, so radiating elements cannot be physically arranged.
Accordingly, such a prior art implements no high-gain phased array antenna applicable to an RF band.
The present invention has been made to solve the above problems, and has as its object to provide a high-gain phased array antenna applicable to an RF band.
To achieve the above object, in a phased array antenna according to the present invention, radiating elements and phase control means are individually formed on a radiating element layer and phase control layer, respectively, to form a multilayered structure as a whole, and the phase control means are phase-controlled by using signal lines and scanning lines arranged in a matrix. With this structure, the radiating elements are eliminated from the phase control layer, thereby reducing an area in the phase control layer which is to be occupied by the radiating elements. In addition, since the wiring lines of the signal line and scanning line for phase control are shared by the plurality of phase control means, the number of signal wiring lines can be greatly reduced.
Further, each driver circuit included in a phase shift unit is formed from a thin-film transistor on a glass substrate, a micromachine switch is used in a phase shift circuit, and the driver circuit and the micromachine switch are housed in a single chip. This reduces an area occupied by these circuit components as compared with the prior art.
Accordingly, since one phase shift unit is formed in a relatively small area, many radiating elements are arranged, in units of several thousands, at an interval (around 5 mm) which is optimal for an RF signal of about 30 GHz. This can implement a high-gain phased array antenna applicable to an RF band.
Furthermore, circuit portions repeatedly arranged in each phase control means, are mounted on first substrates, and the first substrates are mounted on a second substrate on which a phase control layer is formed. This reduces the number of components and the number of connections as compared with the conventional case wherein the circuit components are individually mounted.
With this structure, the number of assembling processes can decrease, and defect inspection can be executed in units of chips, and a yield in the entire phased array antenna can be improved. In particular, the manufacturing cost can be greatly reduced in a high-gain phased array antenna comprised of phase shift units arranged in units of several thousands.